1. Field of the Invention
The present invention generally relates to capacitors. More particularly the present invention relates to a metallized film capacitor having a high viscosity polyurethane oil insulating fluid surrounding at least a portion, and preferably all, of its capacitive element.
2. Description of the Related Art
Metallized film capacitors are typically used for starting and running motors and are also used in lighting applications. The capacitive element of a metallized film capacitor is typically formed by very tightly co-rolling two polymer films having metal layers deposited thereon around a core to form two spaced apart electrodes. Generally, the tightly co-rolled metallized polymer films are placed in a container, which is typically metal. Electrical leads are connected between the metal sprayed ends of the metallized polymer films and terminals mounted on a top. The container is filled with an insulating fluid and the top is sealed to the container. In some capacitors, insulative sheetlike material may be placed in the container between the co-rolled metallized polymer films and the metal container. Also, in some capacitors, a pressure activated circuit interrupter is employed.
The insulating fluid must be compatible with the polymer film forming the metallized film capacitor element in the event that such fluid contacts the film. Compatibility with the polymer film means that the fluid must not act as a solvent towards the polymer film. It is believed that fluids that act as a solvent towards the polymer film, which is typically formed from a polyolefin such as polypropylene, can cause swelling and wrinkling of the film, which is undesirable because it can lead to premature capacitor failure. The insulating fluid should have good heat transfer capability, sufficient viscosity to impede leaking and suitable compatibility with outgassing byproducts caused by corona discharge and clearing phenomena. Also, the fluid should not attack the metal on the metallized polymer film.